Thermoelectric device and method of manufacture

ABSTRACT

A thermoelectric device containing at least one thermoelement formed by powder metallurgical techniques including, but not limited to: hot pressing, hot isostatic pressing, press and sinter and mechanical alloying.

TECHNICAL FIELD

[0001] This invention relates to the field of thermoelectric devicesand, more particularly, to a thermoelectric device wherein the deviceconsists of thermoelements and interconnects of unique design whichmaximize performance while minimizing the use of costly thermoelectricmaterial and further results in a reduction in the number of fabricationsteps.

[0002] In one embodiment of the present invention, a metallic orsemi-metallic support, termed a “wafer”, allows powdered thermoelementmaterial to be processed and facilitates the bonding of these formedelements to their respective interconnection members. Additionally,novel substrate and bonding techniques are also disclosed.

[0003] Other embodiments of the present invention include uniquetechniques relating to thermoelement surface preparation and bonding.

[0004] Lastly, other embodiments of the present invention relate to theapplication of thermoelectric devices in the medical therapy andelectronics thermal management fields.

BACKGROUND OF THE INVENTION

[0005] Conventional thermoelectric devices utilize dissimilar conductivematerials subjected to a temperature gradient across their leg lengthsto create an EMF or electromotive force. This EMF is proportional to theintrinsic thermoelectric power of the thermoelements employed and thetemperature differential between the hot and cold junctions.Alternatively, current may be introduced into the circuit to move heat,absorbing it at one junction, moving it and dissipating it at the otherjunction.

[0006] It is desirable that the thermoelements be of such material thatthe highest EMF is developed for a given temperature differentialbetween the hot and cold junctions. The electrical resistivity andthermal conductivity of the thermoelement in the device should be as lowas possible in order to reduce both electrical and thermal losses andthus increase the efficiency.

[0007] One disadvantage of current thermoelectric devices is the highcost of the semiconducting materials, which yield the highest conversionefficiencies available. A reduction in a thermoelement's cross sectionalarea not only reduces material volume, but increases electricalresistance proportionately. A reduction of element leg length reducesmaterial volume and decreases electrical resistance, but it becomesincreasingly difficult to maintain a temperature differential as thisleg length is decreased to the point where an impracticable heatexchange mechanism is required to remove the heat faster than it isentering the thermoelectric device. This is due to the thermalconduction characteristics of the thermoelement material. Secondly, asleg lengths are further reduced, fabrication of the thermoelementsthemselves becomes increasingly difficult due to the semiconductor'sfragile nature.

[0008] U.S. Pat. No. 3,129,117, granted to Harding on Apr. 14, 1964,discloses a method of manufacturing a thermoelectric element utilizinghot pressing in a direction perpendicular to current flow through thethermoelement.

[0009] U.S. Pat. No. 3,182,391, granted to Charland on May 11, 1995,discloses a process for forming, in one step, a thermoelement with ametallic electrical contact at one end, which comprises consolidatingthe thermoelectric material and metallic contact plate within a diecavity which is then hot pressed and removed from the mold cavity.

[0010] U.S. Pat. No. 3,201,504, granted to Stevens on Aug. 17, 1965,discloses a method of molding a thermoelectric couple in whichdielectric sleeve members are inserted into a mold containing aconductive bottom member, powdered dissimilar thermoelectric material isadded into their respective sleeves, powdered conductor is placed on topof both thermoelements, and pressing and subsequent sintering of theentire assembly yield a solid thermocouple.

[0011] U.S. Pat. No. 3,248,777, granted to Stoll in August of 1966, alsodiscloses a thermal and electrically insulating material in which thethermoelements are cast in cavities within this insulator.

[0012] U.S. Pat. No. 3,264,714, granted to Baer, Jr. in May of 1966,discloses a thermoelectric device in which a block is composed ofthermally and electrically insulating material. This block may be cut toaccept inserted thermoelements or cast from a liquid or other flowableform around the spaced thermoelements and hardened. Additionally, theinterconnecting members are created by electroplating over perforatedmetal and the top faces of each thermoelement to create the junctions.

[0013] U.S. Pat. No. 3,400,452, granted to Emley on Sep. 10, 1968,discloses using hot isostatic pressure (even, compressive pressure inall directions) to provide metallurgical bonding between thethermoelemental material and the walls of a metal tube in which it ishoused.

[0014] U.S. Pat. No. 3,554,815, granted to Osborn on Jan. 12, 1971,discloses a device consisting of a thin, flexible substrate in which“bands” of dissimilar thermoelectric material are disposed on oppositesides of the substrate and perforations within the substrate contain ametallic filler to electrically connect each thermoelement.

[0015] U.S. Pat. No. 3,601,887, granted to Mitchell on Aug. 31, 1971,also discloses the use of hot isostatic pressure to provide bondingbetween the inner walls of a tube and the thermoelectric material.

[0016] U.S. Pat. No. 4,343,960, granted to Eguchi on Aug. 10, 1982,discloses a device consisting of a perforated dielectric substrate inwhich each dissimilar thermoelement is plated, in a pattern, to portionsof both faces and to the walls of each thru-hole.

[0017] U.S. Pat. No. 4,459,428, granted to Chou on Jul. 10, 1984,relates to the design and manufacture of a thermoelectric device whereinthe voids between each thermoelement are filled with a ceramic compoundto absorb thermal expansion. Additionally, copper plates, which willlater comprise the bus bars, are soldered directly to each thermoelementend and then masked and etched to form the discrete interconnects, eachbridging two dissimilar thermoelements.

[0018] U.S. Pat. No. 4,470,263, granted to Lehovee, et al on Sep. 11,1984, relates to a peltier cooled garment in which the heat pumped bythe peltier unit is dissipated to the ambient via cooling fins.

[0019] U.S. Pat. No. 4,905,475, granted to Tuomi on Mar. 6, 1990,relates to a thermoelectric based personal comfort air conditioningunit. Ambient air enters and is split to pass over both the hot and coldfaces of the thermoelectric device. Depending on the desired airtemperature by the user, a movable baffle will distribute the correctamounts of hot and cold air to the individual.

[0020] U.S. Pat. No. 4,930,317, granted to Klein on Jun. 5, 1990,relates to a thermoelectric based localized hot and cold therapyapparatus which includes a heat sink and possibly a fan to dissipaterejected heat.

[0021] U.S. Pat. No. 5,067,040, granted to Fallik on Nov. 19, 1991,relates to the use of thermoelectric cooling to cool computer boardswithin an enclosure. The thermoelectric cooling device is mounted in anopening through a partition for transferring heat out of the sealedenclosure.

[0022] U.S. Pat. No. 5,097,828, granted to Deutsch on Mar. 24, 1992,relates to a thermoelectric based therapy device comprising a heat sinkand fan for dissipating heat moved and generated by the peltier devices.

[0023] U.S. Pat. No. 5,103,286, granted to Ohta on Apr. 7, 1992,discloses a simultaneous sintering and bonding of the thermoelements tothemselves and to their respective interconnection members in theabsence of pressure. Sintering, which is the heating of an aggregate ofmetal particles in order to create agglomeration, does not involvesimultaneous pressure.

[0024] U.S. Pat. No. 5,108,515, granted to Ohta on Apr. 28, 1992,discloses a Bi, Te, Se, Sb thermoelemental material which is pulverizedto a specific particle size and then forming a green molding which isthen sintered.

[0025] U.S. Pat. No. 5,108,788 and U.S. Pat. No. 5,108,789, both grantedto Rauch, Sr. on Jan. 5, 1988 disclose a PbTe thermoelemental materialin which the compound is: melted, chill cast into an ingot, ground to aparticle size of less than 60 mesh, cold pressed to 30-70 kpsi, andfinally sintered.

[0026] U.S. Pat. No. 5,246,504, also granted to Ohta on Sep. 21, 1993,is nearly identical to what is claimed to U.S. Pat. No. 5,108,515.

[0027] U.S. Pat. No. 5,318,743, granted to Tokiai on Jun. 7, 1994,discloses to “presinter” a Bi, Te, Se, Sb thermoelemental material, thenmold the presintered powder and sinter the resultant form also using hotisostatic pressing technology. The actual thermoelements are then cutfrom the sintered bulk.

[0028] U.S. Pat. No. 5,429,680, granted to Fuschetti in July of 1995,relates to a nickel diffusion barrier layer coated directly onto eachthermoelement end.

[0029] U.S. Pat. No. 5,434,744, granted to Fritz on Jul. 18, 1995,discloses a substrated thermoelectric device in which thermoelementalspacing is less than 0.010 inch and thermoelemental thickness is lessthan 0.050 inch. In addition, an improved device is claimed to havegreater than 300 thermoelements and their said thickness is“approximately” 0.020 inch.

[0030] U.S. Pat. No. 5,623,828, granted to Harrington on Apr. 29, 1997,relates to a thermoelectric air cooling device for the passenger of avehicle. A fan, blowing ambient air across both the hot and cold facesof the thermoelectric device, includes a design permitting the cold airto blow onto the passenger while the hot air is exhausted away.

[0031] U.S. Pat. No. 5,800,490, granted to Patz, et al on Sep. 1, 1998,relates to a portable cooling or heating device incorporating athermoelectric assembly comprising: a peltier device, gel pack tointerface with the user along with a fan and radiator to dissipate orabsorb thermal energy from the surrounding air.

[0032] U.S. Pat. No. 5,817,188, granted to Yahatz, et al on Oct. 6,1998, relates to a thermoelectric module comprising thermoelements whosejunctions are coated with bismuth or a bismuth alloy. Additionally, asolder comprising bismuth and antimony is utilized to joint the coatedthermoelements to conductive interconnecting bus bars.

[0033] U.S. Pat. No. 5,890,371, granted to Rajasubramanian, et al onApr. 6, 1999, relates to a passive and active air conditioning systemfor an enclosure housing heat producing equipment. This closed hybridsystem cools the air existing within the heat producing equipmentenclosure housing by recirculating this air across both a heat pipedevice and also a thermoelectric device which transfers the heat to theambient air.

[0034] U.S. Pat. No. 5,981,863, granted to Yamashita, et al on Nov. 9,1999, relates to manufacturing a thermoelement in which moltenthermoelement material is rapidly cooled, powdered and hot pressedwithin a range of time, temperature and pressure in order to reducegrain size, and thus increase material efficiency.

[0035] U.S. Pat. No. 5,987,890, granted to Chiu, et al on Nov. 23, 1999,relates to cooling an electronic component within a portable computerusing a heat pipe or peltier device to move heat from the electroniccomponent to a thermal reservoir, such as a battery.

[0036] U.S. Pat. No. 6,023,932, granted to Johnstone on Aug. 25, 1999,relates to a portable topical heat transfer device comprising athermoelectric unit and heat sink with a fan mounted to the warm side ofthe peltier device.

[0037] U.S. Pat. No. 6,025,544, granted to Macris on Feb. 15, 2000,relates to a block of metallic material into which cavities are formedand filled with thermoelement material. This material is compacted andsintered. The resultant block structure is sliced, electroplated, etchedand mounted to form a thermoelectric device.

[0038] A disadvantage of the existing art is the bond strength betweenthe typically brittle thermoelements and their interconnects. Inaddition, the diffusion of metallic species when these dissimilarmaterials are in contact must be mitigated. Lastly, the bondingstructure, between thermoelement and its respective interconnect, mustnot itself possess a significant Seebeck Coefficient so as not to reducethe performance of the two P and N-type thermoelements.

[0039] A disadvantage to the existing cold therapy technologiesincorporating thermoelectric devices as heat pumps is the means by whichthe pumped heat is dissipated from the hot face of the thermoelectricdevice. Fans and/or heat sinks are cumbersome and reduce flexibility ofthe therapy unit.

[0040] A current disadvantage of the current personal computer orelectronics enclosure cooling art is the complexity and inefficiency ofthe systems resulting in high costs.

SUMMARY OF THE INVENTION

[0041] Accordingly, it is the overall object of the present invention toprovide an efficient thermoelectric device, which minimizes the devicefabrication costs through the simplification of the fabrication processand reduction of materials.

[0042] An additional object of the present invention is to provide athermoelectric device fabrication method in which a metallic orsemi-metallic support (termed a wafer) contains several thru-holes.Dissimilar thermoelectric material is disposed and thermally processedin these thruholes to yield solid thermoelements.

[0043] Again, another object of the present invention is to provide athermoelectric device fabrication method in which the walls of waferthru-holes are coated with either elements or compounds to preventformation of intermetallic compounds between the thermoelements and thewalls during the fabrication of a thermoelectric device.

[0044] Yet again, an object of the present invention is to provide athermoelectric device fabrication method in which a reusable magneticmask is utilized to economically and effectively mask regions of thewafer during chemical processing.

[0045] Still another object of the present invention is to provide aneconomical thermoelectric device fabrication method which improves thebonding between thermoelement and interconnect through anodiccleaning/etching and cathodic surface activation in both acid andalkaline solutions.

[0046] Another embodiment of the present invention is to provide athermoelectric device design wherein the completed device utilizes novelsubstrates and bonding methods which facilitate economical fabrication,yet offer high thermal performance and structural integrity.

[0047] It is another object of the present invention to demonstrate aformula relating the optimal range of thermoelement leg lengths giventhe material's thermal conductivity value. This results in a drasticreduction in the volume of expensive thermoelement material required.

[0048] Still another object of the present invention is to provide animproved thermoelectric-based heating and cooling therapy device whereinthe heat pumped from the source (user) is stored for reuse rather thandissipated to ambient surroundings and eliminates cumbersome heatexchangers.

[0049] Another object of the present invention is also to provide animprovement to existing electronics enclosure air conditioning byutilizing thermoelectric-based conditioning of an input ambientairstream flowing through the enclosure. This allows a thermoelectricdevice to operate efficiently while reducing the internal enclosuretemperature.

[0050] Lastly, the final overall object of the present invention is tocombine all these unique design aspects and individual fabricationtechniques into an overall method of thermoelectric device manufacture,which will yield a device of superior construction and value.

BRIEF DESCRIPTION OF THE DRAWINGS

[0051]FIGS. 1a through 1 m illustrate a method for the fabrication ofthe present invention.

[0052]FIG. 2 is a pictorial representation illustrating the use of asolid, reusable magnetic mask in the fabrication of the presentinvention.

[0053]FIGS. 3a through 3 c illustrate a method for the metallization ofthe thermoelements contained within the present invention.

[0054]FIG. 4 is a sectional view depicting intermetallic layersdeposited on each thermoelement in the present invention.

[0055]FIG. 5 is a graph of the prior art depicting a series of optimalleg length ranges based on a relationship between a thermoelement'sThermal Conductivity value.

[0056]FIG. 6 is a graph illustrating the empirically derived formulabetween a powder metal fabricated thermoelement material ThermalConductivity value and its optimum thermoelement leg length range.

[0057]FIGS. 7 and 8 illustrate one application of the present inventionwherein the apparatus is utilized for heating and cooling therapy.

[0058]FIGS. 9 through 12 illustrate various embodiments for conditioningan airstream through an enclosure containing electronic components.

BEST MODE FOR CARRYING OUT THE INVENTION

[0059] To effectively absorb and dissipate heat, in addition toproviding high electrical conductivity to a thermoelectric device, theinterconnects should be of a highly electrical and thermally conductivematerial such as copper, aluminum, or their respective alloys. Optimallyspeaking, the thermoelement material, composed of a bismuth-tellurium,bismuth-selenium, antimony-tellurium alloy composition, is appropriatelydoped to yield both positive and negative conductivity typethermoelements.

[0060]FIGS. 1a through 1 m illustrate a process flow for the fabricationof the present invention.

[0061] As shown in FIG. 1a, the structure, termed a “wafer” 5, iscomposed of a metallic or semi-metallic material, possibly non-ferrousbased. It contains multiple thruholes formed by either chemical milling(etching), punching or stamping which will contain two dissimilar typesof thermoelement material. The approximate thickness (in the finishedproduct) of this wafer will correspond to the final thermoelement leglength. Due to the processes involved, the wafer thickness isrealistically limited to 0.125 centimeters or less.

[0062] Prior to the dispensation of the thermoelement materials, thewafer's thru-hole walls may be coated with an oxide of the base wafercomposition or other metallics and compounds including: iron oxide,nickel, cobalt, tungsten, molybdenum and carbon. Optimally, the coatingis electrically conductive or semi-conductive.

[0063] Depending upon the thermoelement processing temperatures, i.e.time, temperature and pressure, coupled with the wafer and thermoelementcompositions, an intermetallic layer may form at the thermoelementthru-hole wall interface. The intermetallic, if left on thethermoelement, will degrade the performance of the completedthermoelectric device, therefore, its formation must be prevented, ifformed, must be removed.

[0064] Reference is now made to FIGS. 1b and 1 c wherein two similarmechanisms 9, 16 are utilized to dispense thermoelement material intomultiple thru-holes 7 within the wafer 5. Each mechanism corresponds toa dissimilar type of thermoelement material which is placed in alternaterows of thru-holes.

[0065] Thermoelement material may consist of an alloyed and grown ingotwhich has been pulverized to yield powdered or granular stock, orconsist of a mixture of the powdered or granular metallic elements whichare unalloyed prior to dispensation. Additionally, tablets or pelletsmay be formed with either composition which can also be dispensed intothe wafer's thru-holes.

[0066] In one additional embodiment relating to the preparation ofthermoelement material, a mixture of methanol and boric acid is appliedto the thermoelement powders thereby coating the surface of eachparticle. During the sintering process, any surface oxides present onthe particles are “gettered” by the boric acid, resulting in theformation of borates. This mechanism “cleans' the surface of eachparticle and thus, facilitates the bonding of each particle to theother.

[0067] An empty wafer 5, shown in FIG. 1a, is loaded into thedispensation mechanism 9 of FIG. 1b, mounted below a stencil-like coverplate 10 with apertures 12 corresponding to the thru-holes for one typeof thermoelement material 13. The thermoelement arrangement of thepresent invention consists of alternating P and N-type thermoelements.The thermoelement material 13 is then poured into the stencil reservoir14 where it is bladed across the stencil surface by a doctor blade orsqueegie-like instrument 15. The wafer thickness plus the stencilthickness allow for the correct volume of powder to be dispensed intothe thruholes of the wafer.

[0068] When the entire surface of the wafer has been filled and bladed,the filled holes are then compacted with either a matrices of metallicpress pins or a flat elastomeric pad, both of which compact the powderthru the stencil apertures and down to the wafer surface.

[0069] Once compacted, the wafer is removed and transferred to thesecond dispensation mechanism 16 in FIG. 1c, which deposits and compactsthe other dissimilar type thermoelement material 19. This mechanismoperates identically to the previous unit in FIG. 1b, however, itsstencil apertures 17 correspond to the unfilled thru-holed 18 whichremain with in the wafer.

[0070] The resultant wafer 18, filled with dissimilar typethermoelements 20, 22, can be seen in FIG. 1d.

[0071] The wafers must now be processed thermally with powdermetallurgical techniques in order to create interparticulate bonding,resulting in solid, dense thermoelements. The thermally based powdermetallurgical techniques include: hot pressing, hot isostatic pressing,press and sintering, and mechanical alloying. The first two processesinvolve the simultaneous application of heat and pressure. Press andsinter technology typically applies heat and pressure in separate steps.Lastly, mechanical alloying can incorporate heat and pressuresimultaneously or as separate, discrete steps.

[0072]FIG. 1e discloses a method of hot pressing multiple wafersutilizing sheets of heat resistant material 24. Compressive force isapplied to each thermoelement via their exposed surfaces. A material,such as aluminum or other metallic sheet or foil, is stacked alternatelywith the filled wafers, such that, all exposed thermoelements 20, 22 arecovered by the sheet material 24. Pressure and heat are applied to thestack by means of a heated press seen in FIG. 1f. The heat resistantmaterial will deform under this heat and pressure and transfercompressive force to each thermoelement from both faces of the wafer.

[0073] In one embodiment of the present invention, a heat resistantmaterial envelops each wafer face and then is subjected to hot isostaticpressure. This process utilizes a fluid or gas under extreme pressure toapply compressive force to the wafer from all directions. The force isagain transferred through the heat resistant material to each face ofthermoelements resulting in a high degree of density.

[0074] In another embodiment of the present invention, the press andsinter technique is utilized to densify the thermoelements. Thistechnique, essentially a “pressureless” sinter process, eliminates therequirement of a covering material in order to transfer pressure to eachthermoelement face.

[0075]FIG. 1g depicts the wafer 18 and heat resistant covering material24 following either the hot pressing or hot isostatic operation. Theheat and pressure has densified each thermoelement 20, 22 therebyreducing their respective thicknesses.

[0076]FIG. 1h depicts the wafer 18 after the removal of the envelope orcovering material 24. Prior to the bonding of interconnection members,the thermoelement faces must be cleaned and activated to accept ametallization layer to facilitate bonding and mitigate diffusion betweeninterconnect and thermoelement.

[0077] Each type of thermoelement material behaves differently to aparticular surface etchant/cleaner and activator requiring a uniquechemistry and process for each material. Both types, however, are bestetched/cleaned and activated electrochemically, in that an electricpotential is applied to the parts while in a conductive, corrosivesolution.

[0078] In one embodiment, the wafer is immersed into an alkalinesolution, preferably sodium or potatassium hydroxide-based. A positiveelectric potential (voltage) is applied to the wafer (the anode) and anegative potential is applied to a metallic member or electrode(cathode) which is also immersed in the solution. The wafer with itsthermoelement surfaces are exposed to the electric current via thesolution, causing a surface etching of the elements. The wafer is thenrinsed and neutralized to remove the surface residue and expose cleanthermoelement surfaces.

[0079] In another embodiment, the wafer is immersed into a solutioncontaining chromic acid. The wafer is immersed and electrified as in theprevious embodiment.

[0080] Following the surface etching and cleaning of the thermoelements,a metallic layer must next be deposited. The bismuth-tellurium alloythermoelement materials, however, easily forms surface oxides, creatinga passive condition. Therefore, it is necessary to activate thesesurfaces in order to achieve an adherent metal layer.

[0081] Cathodic activation, wherein the wafer is connected to a negativeelectric potential (cathode), has been found empirically to effectivelyactivate the tenacious thermoelement surfaces. The wafer is immersedinto an acidic solution, preferably containing sulfuric acid, andconnected to the negative potential terminal of a power supply. Ametallic electrode, also immersed, completes the electrical circuitthrough its connection with the positive terminal of the power supply.Optimally, the wafer is subjected to an electric current density greaterthan 150 amps per square foot of total negatively charged surface areaexposed in the solution.

[0082] Immediately following the cathodic activation step, the entirewafer is subjected to either electro less or electroplating, as seen inFIG. 11, which deposits a continuous metallic layer 25 over the entirewafer surface the electroplating and cathodic activation electricpotential is to be applied prior to immersion so as to not passivate, oroxidize the thermoelement surfaces.

[0083]FIG. 1j introduces a metallic sheet 30 which is soldered 31 toeach face of the wafer 18 via the metallized layer 25. The metallicsheets 30, preferably comprised of highly thermal and electricallyconductive material, will ultimately comprise the interconnectionmembers.

[0084] In one embodiment, a molten or semi-molten metallic sprayingprocess, such as plasma or flame spraying is utilized to build ametallic deposit in lieu of the metal layers 25, 30, 31 plated and/orsoldered in FIGS. 1l and 1 j.

[0085] Within FIG. 1k, it can be seen that an etch resistant mask 34 hasbeen applied over select regions of the metallic sheet 30 in order toprotect the eventual interconnection members from chemical attack.Typically, a screen or stencil preinked mask, or “resist”, is employed,which may later be stripped chemically.

[0086] In one embodiment of the presents invention, a reusable, solidmagnetic mask 40 (FIG. 2) is utilized on both faces of the wafer 18 inlieu of printed resists. The masks are die or laser cut from flexiblemagnetic material composed of ferrites in a polymer binder. These maskscan be utilized in both plating and chemical etching operations.

[0087] As seen back in FIG. 11, the unmasked regions of the metallicsheet 36 have been subjected to a selective chemical etchant to removeregions of the metal layers and wafer in order to create completedthermocouples 45.

[0088] Lastly, FIG. 1m contains the series thermocouples 45, minus theetch mask 34, ready to be mounted to a structurally supportingsubstrate. Bonding may be accomplished through the use of a thermallyand/or electrically conductive adhesive, such as an epoxy. Additionally,mechanical clamping between two substrates may also be employed.

[0089] In one embodiment, a perforated metallic substrate is utilized inorder to reduce weight and also to facilitate handling of the fragilethermocouples following the etching step.

[0090] The metallic substrates, whether perforated or solid, may besubjected to an anodizing or conversion coating process to create adielectric surface layer in order to prevent any electrical “shorting”between the mounted thermocouples.

[0091]FIGS. 3a through 3 c illustrate an alternate embodiment wherein abismuth layer 26 is either electrolessly (immersion) or electroplated oneach thermoelement surface.

[0092]FIG. 3a depicts a filled wafer 18 prior to metallization.

[0093] In FIG. 3b, the bismuth layer 24 deposited onto the wafer 18 isthen reflowed, or melted and solidified in order to increase the bondstrength to the thermoelements. This reflow technique creates an alloyedbond which penetrates each thermoelement, resulting in higher bondstrength over standard metallization techniques.

[0094] Reference is now made to FIG. 3c, wherein the cathodic activationand electroless/electroplating techniques, from the previousembodiments, are employed to deposit an additional adherent metal layer28 over the reflowed bismuth layer 26. This metal layer 28 permits theattachment of the interconnection member layers via soldering whilemitigating any diffusion between dissimilar materials.

[0095] Next, as seen in FIG. 4, the completed series thermocouples 45may contain an intermetallic layer 50 bonded along the leg lengths ofeach thermoelement 20, 22. If left, this layer will degrade theperformance of the thermocouples by creating a partial electrical shortbetween the hot and cold junctions.

[0096] In one embodiment electrochemical removal is employed byimmersing the thermocouple assembly into an alkaline or acidic solutionand applying either a positive or negative potential (voltage) to thisassembly. An immersed electrode completes the electrical circuit byaccepting the voltage polarity opposite that of the thermocoupleassembly. After removal from the solution, the assembly is chemicallytreated and rinsed to eliminate any residues. One effective solution forthe intermetallic removal contains chromic acid.

[0097] With respect to FIG. 5, reference is made to U.S. Pat. No.6,025,554, granted to Macris Feb. 15, 2000, wherein the prior artdepicts the derived relationship between any thermoelement's leg lengthand its particular thermal conductivity value. When this value is givenin watts/centimeter per degress Celsius, for any thermoelectricmaterial, the optimum thermoelement leg length 54 is equal to thatparticular thermal conductivity value with a leg length tolerance.

[0098] As seen in FIG. 6, an optimized range of thermoelement leglengths 55 is disclosed, given the thermoelement material's thermalconductivity value (K), in watts/centimeter per degree Celsius. Throughthe use of thermoelements formed by powder metallurgical techniques,such as: hot pressing and sintering, hot isostatic pressing andmechanical alloying, an empirically derived formula was developed. Eachthermoelement has a leg length range 55, in centimeters equal to:

[0099] (K+0.026 centimeters) to (K+0.061 centimeters).

[0100] Reference is now made to FIG. 7 wherein an application ofthermoelectric devices is depicted. A wearable heating and coolingtherapy device 65, consisting of: thermoelectric devices 60, a thermallyconductive compliant layer 61 interfacing the wearer, a flexiblethermally insulating layer 62 and a flexible thermal storage medium 63.

[0101] When it is desirable to cool selected portions of the wearer'sbody (FIG. 8), the thermoelectric devices will “pump” heat away from theuser via the compliant layer 61 to the thermal storage medium 63. Theinsulating layer 62 maintains the temperature differential, establishedby the thermoelectrics 60, between the wearer and the storage medium 63.A reversal in the polarity will cause the stored thermal energy in thestorage medium 63 to be transferred to the user when heat therapy isdesired.

[0102] In one embodiment, the thermal storage medium 63 may be comprisedof a phase-change material which will accommodate additional thermalenergy (per pound of medium) without significantly raising thetemperature of the thermal storage medium. This is accomplished throughthe transformation from one “phase”, or form, to another when thermalenergy is absorbed. For example, a liquid phase change material (liquidat room temperature), may absorb an order of magnitude or more thermalenergy (before its full phase transformation to a gas phase) than anequivalent weight quantity of non-phase change material withoutincreasing its actual temperature.

[0103] Other embodiments include the use of polymer-based,elastomer-based or ceramic-based materials in the construction of thethermal storage medium 63.

[0104] Next, as seen in FIGS. 9 through 12, various embodiments aredisclosed for an additional application of thermoelectric deviceswhereby the incoming airstream, through an electronics containingenclosure, is conditioned, or cooled.

[0105]FIG. 9 displays the current construction and action of the priorart. An enclosure 70, which may house various electronic components andassemblies 72, 73, typically draws ambient air 71 throughout theenclosure to aid in the dissipation of heat generated by the electronics72, 73. A fan assembly 75, usually located within the enclosure 70,draws this ambient air 71 past the electronics and exhausts the heatedairstream 74 back to ambient.

[0106] Within FIG. 10, an assembly comprising a thermoelectric device80, a hot face heat sink 82 and cold face heat sink 81 is mounted infront of the ambient air inlet 69 to the enclosure 70. Ambient air 71 isactively drawn through the cold face heat sink 81 by the fan assembly75. The thermoelectric device 80 cools this incoming ambient airstream71, thereby dropping the air temperature upon entry into the enclosure.The cooled airstream 77 increases the thermal transfer efficiencybetween the electronics 72, 73 and the airstream 77. The heated air 74is exhausted back to ambient. The hot face heat sink 82 dissipates itspumped thermal energy passively to ambient.

[0107]FIG. 11 illustrates an embodiment of the present invention wherebythe heated airstream 74, exhausted by the fan assembly 75, is ducted andblown across the hot side heat sink 82, of the thermoelectric device 80,increasing the heat dissipation of this 82 to ambient.

[0108]FIG. 12 depicts an additional embodiment wherein a fan assembly 71is mounted “upstream” from the thermoelectric device 80 and heat sinks81, 82. The ambient airstream 71 is pushed through the heat sinks 81, 82and the enclosure 70 where the heated airstream 74 is exhausted.

1. A thermoelectric device containing at least one thermoelement formedby powder metallurgical techniques wherein each thermoelement has a leglength range, in centimeters, equal to: (K+0.026 centimeters) to(K+0.061 centimeters), wherein K is the thermoelement material's thermalconductivity value, given in watts/centimeter per degree Celsius.
 2. Athermoelectric device design, providing at least one wafer containing atleast two through-hole cavities to accept thermoelements, wherein thewafer thickness is equal to or less than 0.125 centimeters.
 3. Athermoelectric device design, as in claim 2, wherein the wafer iscomposed of a metallic material.
 4. A thermoelectric device design, asin claim 2, wherein the wafer is composed of a non-ferrous metallicmaterial.
 5. A thermoelectric device design, as in claim 2, wherein thewalls of the wafer through-holes are coated with an electricallyconductive material.
 6. A thermoelectric device design, as in claim 2,wherein the walls of the wafer cavities are oxidized to mitigate theformation of an intermetallic layer on the thermoelements.
 7. A methodof manufacturing a thermoelectric device, including at least onethermoelement, one heat rejecting interconnection member, one heatabsorbing interconnection member, one wafer containing at least twothrough holes, each containing dissimilar thermoelectric materialcomprising the steps of: a. Simultaneously dispensing one type ofthermoelectric element materials to at least two wafer through holes; b.Simultaneously cold compacting more than one thermoelement with thewafer; c. Covering each wafer face with a heat resistant material; d.Apply hot isostatic pressure to the entire covered wafer; e. Removingthe covering; f. Cleaning and electrochemically activating the entirewafer surface including the exposed faces of each thermoelement; g.Plating the entire wafer surface including all exposed faces of eachthermoelement; h. Bonding a metallic sheet to each face of the wafer viathe plated layer; i. Chemically removing part of each metallic sheet andall of the wafer material; j. Mounting the completed device to asubstrate.
 8. A method of manufacture, as in claim 7, wherein the waferis a metallic material.
 9. A method of manufacture, as in claim 7,wherein the thermoelement material is in powder form.
 10. A method ofmanufacture as in claim 7, wherein the thermoelement materials is intablet form.
 11. A method of manufacture, as in claim 7, wherein step(a) involves the use of a squeegie for the dispensation of thethermoelement powders.
 12. A method of manufacture, as in claim 7,wherein the step (c) covering is a metallic foil.
 13. A method ofmanufacturing, as in claim 7, wherein the thermoelement material in step(a) is a mixture of metallic elements which, following step (d) willbecome the resultant P and N-type thermoelement compounds.
 14. A methodof manufacture, as in claim 7, wherein step (d) involves the use ofpressureless sintering (heat only).
 15. A method of manufacture, as inclaim 7, wherein step (g) utilizes a metallic spraying process in lieuof the electroplating and/or metallic sheet in steps (g) and (h)respectively.
 16. A method of manufacture, as in claim 7, which utilizesa conversion coated (anodized) substrate.
 17. A method of manufacturinga thermoelectric device, including at least one thermoelement, anenvelope or covering, one wafer containing at least two through holes,each containing dissimilar thermoelectric material wherein a pressurizedliquid gas is utilized to compact the thermoelements by applyingpressure against the envelope which is in direct contact with eachthermoelement.
 18. A method of manufacturing a thermoelectric device,including at least one perforated metallic substrate with two or morethrough holes (filled with dissimilar thermoelement material) in whichthe completed device is bonded to a perforated metallic substrate.
 19. Amethod of manufacture, as in claim 18, which utilizes a conversioncoated (anodized) substrate.
 20. A method of manufacture, as in claim18, in which the bonding is accomplished through the use of an adhesive.21. A method of manufacturing a thermoelectric device, including atleast one thermoelement, reusable magnetic mask material and at leastone wafer wherein the prepatterned magnetic mask is placed on each faceof the wafer for subsequent chemical processing.
 22. A method ofmanufacturing a thermoelectric device, including at least onethermoelement, one wafer containing at least two through-holes, eachcontaining thermoelement material and at least one sheet of deformablematerial wherein the wafer and sheet of deformable material are stacked,such that the deformable material interfaces the exposed thermoelementfaces, and subjected to heat and pressure, thereby causing thedeformable material to deform and compress the thermoelement materialinto the wafer through-holes.
 23. A method of manufacturing athermoelectric device, as in claim 22, wherein the sheet of deformablematerial is comprised of aluminum.
 24. A method of manufacturing athermoelectric device, including at least one thermoelement, one wafercontaining at least two through-holes, each containing P and N-typethermoelement material wherein both the P and N-type thermoelementmaterials are hot isostatic pressed simultaneously.
 25. A method ofmanufacturing a thermoelectric device, as in claim 24, wherein both theP and N-type thermoelement materials are hot pressed simultaneously. 26.A method of manufacturing a thermoelectric device, including at leastone thermoelement, in which the surface preparation of eachthermoelement for interconnection bonding comprises: a. Immersion of thethermoelements into an alkaline solution; b. Making the thermoelementsanodic through the application of an external positive polarity voltageto the thermoelements; c. Completing the electrical circuit within thealkaline solution by applying the external negative voltage polarity toa metallic member, now made cathodic; d. Removal of thermoelements fromthe alkaline solution and removal of their remaining surface layerresidue chemically.
 27. A method of manufacturing, as in claim 26,wherein the alkaline solution is a solution containing chromic acid. 28.A method of manufacturing a thermoelectric device, including at leastone thermoelement, in which the surface preparation of eachthermoelement for interconnection bonding comprises: a. Immersion of thethermoelements into an acidic solution; b. Making the thermoelementscathodic through the application of an external negative polarityvoltage to the thermoelements; c. Completing the electrical circuitwithin the alkaline solution by applying the external positive voltagepolarity to a metallic member, now made anodic; d. Plating a metalliclayer on each surface of the thermoelements.
 29. A method ofmanufacturing, as in claim 28, wherein the acidic solution is a solutioncontaining sulfuric acid.
 30. A method of manufacturing, as in claim 28,where the thermoelement surfaces are subjected to a current densitygreater than 150 amps per square foot of negatively charged surface areain the solution.
 31. A method of manufacturing, as in claim 28, whereinthe electrical potential applied to the thermoelements in steps (a)through (d) is applied prior to immersion of the thermoelements intoeach solution.
 32. A method of manufacturing a thermoelectric device,including at least one thermoelement comprising: a. Depositing a bismuthlayer on each junction face of the P and N-type thermoelements; b.Melting and solidifying the bismuth layer; c. Depositing a metalliclayer on the bismuth layer.
 33. A method of manufacturing, as in claim32, wherein step (a) utilizes plating to deposit the bismuth layer. 34.A method of manufacturing a thermoelectric device, including at leastone thermoelement, in which the removal of surface layers between thehot and cold junctions of each thermoelement comprises: a. Immersion ofthe thermoelements into a corrosive solution; b. Making thethermoelements anodic through the application of an external positivepolarity voltage to the thermoelements; c. Completing the electricalcircuit within the corrosive solution by applying the external negativevoltage polarity to a metallic member, now made cathodic; d. Removal ofthermoelements from the corrosive solution and removal of theirremaining surface layer residue chemically.
 35. A method ofmanufacturing, as in claim 34, wherein the solution contains chromicacid.
 36. A method of manufacturing, as in claim 34, wherein step (b)polarity is negative and the step (c) polarity is positive.
 37. A methodof manufacturing a thermoelectric device, including at least onethermoelement, wherein the thermoelement materials, in powder form, arecoated with boric acid prior to thermal processing (sintering, hotpressing, etc.) to getter surface oxides.
 38. A wearablethermoelectric-based heating and cooling therapy apparatus design,including at least one thermoelectric device and a thermal storagemedium wherein one face of the thermoelectric device interfaces thesource to be heated or cooled (wearer) and the opposite face of thethermoelelctric device interfaces a thermal storage medium.
 39. Awearable thermoelectric-based heating and cooling therapy apparatusdesign, as in claim 38, wherein the thermal storage medium is apolymer-based material.
 40. A wearable thermoelectric-based heating andcooling therapy apparatus design, as in claim 38, wherein the thermalstorage medium is a elastomer-based material.
 41. A wearablethermoelectric-based heating and cooling therapy apparatus design, as inclaim 38, wherein the thermal storage medium is a ceramic-basedmaterial.
 42. A wearable thermoelectric-based heating and coolingtherapy apparatus design, as in claim 38, wherein the thermal storagemedium comprises a phase change material.
 43. A thermoelectric-basedsystem design for conditioning the ambient air drawn through anenclosure comprising: a. Establishing an airflow through the enclosure;b. Conditioning the input airstream to the enclosure with athermoelectric device.
 44. A thermoelectric-based system design forconditioning the ambient air drawn through an enclosure, as in claim 43,wherein the enclosure houses heat generating electronics.
 45. Athermoelectric-based system design for conditioning the ambient airdrawn through an enclosure, as in claim 43, wherein the enclosure housesheat generating electronics.
 46. A thermoelectric-based system designfor conditioning the ambient air drawn through an enclosure, as in claim43, wherein the enclosure's airstream exhaust, or discharge air, isdirected over one face of the thermoelectric device.